Transistor test set



Oct. 6, 1959 A. J. RADCLIFFE, JR

TRANSISTOR TEST SET 2 Sheets-Sheet 1 Filed Dec. 2l. 1955 BOmmm 9v:

Oct. 6, 1959 A. J. RADCLIFFE, JR 2,907,954

' TRANSISTOR TEST SET Filed Dec. 21, 1953 2 Sheets-Sheet 2 FIG. a m FIG. 3 m (POS. n ,(POS. 2) I I l l l ulisse -es soo, 11 50o,

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\ IZIOQ B4 D (P054) I I l United States Patent O 2,907,954 TRANSISTOR TEST SET Arthur J. Radcliffe, Jr., La Grange, Ill., assignor to International Telephone and Telegraph Corporation, a corporation of Maryland Application December 21, 1953, Serial No. 399,560

9 Claims. (Cl. 324-158) vThis invention relates to a transistor test set. Its principal object is to provide a simple, reliable, and economical test set for use-in determining the important characten'stics of aV transistor. y

GENERAL DESCRIPTION Either of these point contacts, with the base element,V

forms a hal-f-wave rectifier (or diode) having a forward direction of .ow which depends uponl which of the two types (N or P) of semi-conductor is used as the base. An N-type 4base comprises the negative diode element, and a P-type base comprises the positive diode element.

,A junction transistor triode may comprise a single semi-conductor crystal in the form of a three-section bar, with the `center section comprising the common, or base, electrode. The Ibarrier portions, or films, which separate the 'base portion from the two end portions have rectifying qualities, wherefore the base portion and either end portion comprises a diode having a directional rectifying action Iwhich depends upon the relative crystalline structure of the sections. The two end sections are similar in structure and are either both negative, or are both positive, in rectifying action, with respect to the center,

orybase section. y

From a circuit standpoint, ythe three electrodes of a transistor triode are termed respectively` emitter, base, and collector, the base being the com-mon electrode.

Transistor triodes` are further classified, according to diode polarity, as of NPN type or of PNP type. In the NPN type, both emitter and collector are negative with respect to the base, while both the collector and the emitter are positive with respect tothe base in the PNP type.

As a transistor is commonly used, Lthe emitter diode is biased by a direct-current rwhich ows in the forward direction therethrough and the collector diode is biased by a direct-current (the power current) which flows in the reverse direction therethrough. They emitter diode is in the signal-input path, while the collector diode is in the signal-output path. Signal-induced variations in the forward biasing current through the emitter diode causes current and/or voltage Variations in the reverse biasing current through the collector diode of a higher power than the power required to be expended in the'emitter diode to produce them, which characteristic gives rise to the signal amplification obtainable in the transistor.

Thefollowingsix operational characteristics are generally considered to 'be of test importance in ascertaining t 2 whether any selectedvtransistor will perform satisfactorily in a given circuit situation:

(l) Grounded-base current-gain factor (Alpha or A)- the ratio of output signal current through negligible external output impedance to input signal current, taken with the ibase grounded and the emitter isolated from ground.

(2) Grounded-emitter current-gain factor (Beta or B)-the ratio of output signal current through negligible external output impedance to input signal current, taken with the emitter groundedand the 4base isolated from ground.

(3) Base resistance (Rb)-the internal resistance of the base electrode.

(4) Emitter resistance (Re)the signal-current resistance of the emitter diode, less the base resistance Rb, being the internal emitter electrode resistance to signal current, plus the emitter barrier resistance to signal current.

(5) Collector resistance (Rc)the signal-current resistance of the collector diode.

(6) Effective series resistance (Res)-the effective signal-current resistance of the two diodes in series.

A specic object of the invention is to provide a transistor tester Vwhich will permit Iany or Aall of the foregoing six oper-ating characteristics of ia transistor triode to be obtained by simple and reliable tests.

It has been chosen to illustrate the invention as embodied in a test set for'testing a transistor triode of either NPN or PNP type under operating conditions by applying normal operating current through A.C.-isolating choke coils to the respective electrodes, while making parallel alternating-current signal connections to the electrodes through D.C.isolating condensers.

An important feature of the invention is that the necessity for .a precisely calibrated current or Voltage meter is avoided, and precision is enhanced, by a `comparison 'arrangement wherein `any resistance value under observation is directly compared with a calibrated precision slidearm resistor.

A further feature is that the test set is readily positioned lfor any one of the several tests of a transistor connected thereto, and that the necessary measuring and comparison adjustments may be made while thetest set remains in that selected position. It has been chosen to employ a multi-brush rotary switch for positioning `the test set, such switch being manually operable to positions corresponding respectively to the desired test positions of the test set.

A further feature is that the test set is arranged to employ standardized voice-frequency generating, amplifying, and indicating apparatus. f

Other objects and features will become apparent as the description progresses. Y

THE DRAWINGSV 'arrangements specific respectively to test positions l to 6y o-f the test set of Fig. l.

The `apparatus of Fig. l is preferably all mounted in the same cabinet, or behind the same panel, with thev manual control devices controllable from the front, from.

which position the-visual indicating devices are-visible. Fixed test terminals E, B, and C, as well as E', B', and C', are also preferably accessible from the front of the device. Terminals E, B, C detachably receive a junction transistor TR for test, whose prongs or terminal conductors connect respectively thereto, and ,terminals Patented Oct. 6, 1959" 3 E', B', C', detachably receive a point-contact transistor for test. Conductors 2 to 4 lead from the test terminals E, B, and C to the illustrated test apparatus.

The visual indicating instruments comprise (1) the checking DLC. voltrneter 300' connectable to test conductors 3 and `4- by push key K-3', (2)Y the A C. voltmeter 40o, which is the principal rest-indicating instrunient, and (3) the' monitor 600 Whichis used to show the waveform of the' signals responded to by the voltrneter 400. Generator 500 contains a 100G-'cycle oscillator 501 for supplying 100G-cycle signal current for test purposes, and to exerciseV the"l necessary sweep con-trol over monitor 600.

Supply' unit 200 comprises the DC.- source of biasing current for the transistor under test. The associated key K-l has contact sets 1 and 2 for reversing the out?- put Wires of unit 20'0" according to the polarity type' (NPN or PNP) of the transistor being tested. Contact sets 3 to' 8 of key K-'l arev used to reverse the connections to each of the high-'cz'xpacityr electrolyti'cv D.C.blocking condensers 104 to 1-06, whereby each such condenser' always has the same DLC;v polarity across its terminals. Highinductance choke coils 101 to 103 are to prevent the now to ground of A.C. signal currents reaching wires S to I0.

The six position rotary selector switch 120 is controlled by knob 121. It has nine brushes B1 to B9 for connecting the conductors 5 to 7 and associated conductors each to -a separate circuit point for each of the six test postions of the test set. For this purpose', there are shown six horizontal rows of brush contacts, rows P-'l to P-6. The brushes (shown in position l) are caused to contact the one of the horizontal rowsl P-1 to P-6 which corresponds to the desired test position.

Device PR isV the precision slide-arm resistor previously referred to; key K-4 is used to change from comparing to tes-ting; and resistors 11117, 112, and' 1-14v to 116 comprise precision resistors usedl in the testing and comparing operations as will be eiipljained. l l

Functionally, the foregoing apparatus of Fig.- 1 cornprises two groups of circuits, a signal: group and a bias group. The bias groupl of circuits establishes directcurrent operating" conditions for the transistor by way of conductors 8 t'o1`0' and choke coils 101 to 103, while the signal group of circuits provides alternating-current circuit connections through' conductors 5 toV 7 and co-ndensers 104'y to for measuring the characteristics of the transistor under test.

The group of signal-current measuring circuits includes the compare-test key K-4, the calibrated precision resistor PR, the 100G-cycle signal generator 500, the altermating-current voltmeter 400, and the associated monitor 600.

DETAILED DESCRIPTION The invention having been described generally, a detailed description follows.

(A) Junction type NPN test i tothe emitter and collector electrodes of TR from the negative source 1 andv the positive source 202, respectively, by way of resistors 203 and 204, meters 205l andl 206', normal contacts I1 and 2 of `key KA, choke coils 101 and 103, cor'iduc't'orsy 2 and v4, and test terminals E and C. The two bias-current paths have a common return path to ground through the base electrode of TR, terminal B, conductor 3', and choke coil `102. Resisters 203 and' 204 are now adjusted until' meter 205y shows the desired negative emitter current and meter 206 shows the desired positive collector current. The' negative emitter current is in the `forward direction through lthe emitter diode `of TR, while the positive co1- lector current is in the reverse direction through the collector diode of TR, in accordance with the noted usual circuit use of a transistor. Incidental to the adjustment of resistors 203 and 204, key K-3 may be closed temporarily to enable D.C. volt'meter 300L (including D.C. amplifier 302 and meter 301) to show the D.C. voltage across the collector diode (terminals B- and C), asa precautionary checking operation.

With normal direct current now flowing throughy the elements of transistor TR as described, six tests of' TR may be performed as follows:

Test 1. Grounded-base current-gain factor A.-Re ferring to Figs, 1 and 2, with selector switch 120 in position l as shown (brushes B1 to B9 on contacts P-l), th'e test set is in posi-tion` for the grounded-base cur-'rentgain factor A (or Alpha) to be' ascertained.

In the generator 500, lOOOIcycl'e current is supplied hy oscillator 501, through amplifier 502,y to step-down trans"-l former 504. For tests l, 2, 5, andl 6, generator 500 is used as a low-impedance, low-voltage generator to provi'de a" uniformI voltage' source during the necessary testingv and comparing operations (hereinafter described): in# cidental to these four tests. Generator key K-Sl isl con# sequently left inits illustrated normal position for these" four tests, being operated only for tests 3 and 4 to' supply a higher generator voltage.

Continuing withI test 1, G-cycle signal current now flows through the emitter diode of TR from the seconda-ry windingv of transformer 504 of generator 500' through the normal contacts of K-S, and generator wires 1.42" and 143'. From wire' 142, the path to the emitter electrode is through brush B1- of switch 120, conductor 5, normal contact 4- of key K-1, condenser 104, normalI contact 3 of K-l, conductor' 2, and throughy terminal E to the left-hand, or emitter electrode of Thence, the flow s'y through the' base electrode of TR, terminal B, conductor 3', normal contact 5y of K-l", condenserr105, normal contact 6 of K-I, conductor 6', and brushv B2' of switch to ground. Thence, the' main return ow is through the 10d-chin resistor 116, brush B9, and over conductor 143 to generator 500. The 10,000-ohrn resistor PR is in parallel withI resistor 11'6 through brushes and B8, the parallel resistance of PR and 116 being 100y ohms for test convenience.

The 100G-cycle signal current flowing through the emitter diode over the traced path comprises A'.C.\variations superimposed on the normal D.C. emitter bias current over Wire 8Ll These variations cause corresponding variations in the resistance` of the collector barrier of TUR, through which the collector bias` current is flowing. The result is a 100G-cycle collector signal current which flows in a circuit path from the right-hand (collector)A electrodel of transistor TR, through'l terminal C, conductor 4, normal contact 7 of K-L condensergl, normal' contact 8 of Kf 1, conductor 7, brush' B3', lO-ohnr resistor 112, to ground. Thence, the return ow is Ithrough brushA B2, conductor 6, normal contact 6 of Kfl, condenser 105, normal contact 5 of K-1, conductor 3, terminal B and base electrode, to the collector electrode of TR. l

A.C. voltmeter 400 has one input conductor grounded as shown, itsl other input conductor being 141". In' 400, these input Wires lead through adjustable attenuator 401, amplifier 402, and rectifier 403 to meter instrument 404. Externally, input wire 141 of voltmeter 400 leads through brushes B5` and B6 (position 1') tothe lever arm of key K-4.

In order to obtain a test reading on voltmeter 400'V of the collector signall current, key K-4 is now operated. r["he lever arm thereof transfers the voltmeter-input wire 141 to the ungrounded terr'nin'all of the lO-ohm resistor 112, which isl in the previouslyv traced GollectoncuirettV path.

' voltage amplifier 402.

The voltage drop to ground across resistor 112 is thus impressed on input wire 141 of voltmeter 400', which is preferably of such high input impedance that the current it draws is negligible. This signal Voltage passes through items 401, 402, and 403 to meter 404, which gives a voltage reading depending on the value of the collector signal current through 112.

The signal voltage, as amplified by 402, is supplied to monitor 600, whereat it passes through amplifier 601 to reach the cathode-ray display tube 602. This tube is also controlled by the 1000-cycle sweep generator 603, kept in step by a portion of the output of oscillator 501 in generator 500. Tube 602 thus displays the wave form of the collector current as shown by the output The collector signal current is adjusted to a suitable non-clipping, or non-distortion, value by adjusting emitter signal current, which is effected by adjusting the voltage output to the emitter circuit by generator 500. For this purpose, a gain-control device (not shown) is provided in amplifier 502, and is now adjusted until tube 602 of the monitor 600 shows a sine Wave input to voltmeter 400.

Attenuator 401 is now adjusted to give a convenient test value to the reading on meter instrument 404 of meter 400. j

Having noted the adjusted test reading (for collector signal current) on instrument 404 of voltmeter 400, the operator now releases the key K-4 and adjusts precision resistor PR to give the same reading at voltmeter 400 for the emitter signal current. When key K-4 is released, it disconnects the voltmeter-input conductor 141 from resistor 112 and reconnects it to the slide arm of resistor PR. The 10,000-ohm resistor PR, in parallel with lOl-ohm resistor 116, comprises a U-ohm resistor in series with the emitter signal-current path hereinbefore traced. The voltage drop per unit signal current through this 10Q-ohm resistance path is ten times the drop per unit signal current through the l0ohm resistor 112 in the collector signal-current path, thereby per-` mitting a current-gain factor of ten to be observed when the slide arm of PR is at its B8 position. For this test, this value is higher than that of any transistors commonly produced.

With the B7 terminal of PR now grounded, and assuming that the slide arm is 4calibrated decimally from Oat its B7 terminal to l at its B8 terminal (as 0.0, 0.1, 0.2, .etc. 0.09, 1.0), the setting of slide arm PR to supply the same voltage to wire 141 (to give same reading at 400) as was supplied to it across resistor 112 with key K-4 depressed, must be multiplied by ten to give the gain factor of this test.

The key K-4 may be depressed and released as many times as desired to check the current-gain factor A indicated by the above setting of the slide arm of PR.

'T est 2: Grounded-emitter current-grain factor B.-Re fering to Figs. 1 and 3, the knob 121 is rotatedto its position 2 for test 2, thereby rotating brushes B1 to B9 from their contacts P-1 to their contacts P-2. With generator key K-S left in its normal position, the associated circuit arrangement is in readiness for tests to ascertain the grounded-emitter current-grain factor B (or Beta).

The 1000-cycle input signal current nowows from generator 500 to the base electrode of transistor TR, over conductor 142 and brush B2. Thence the return ow of input signal current may divide, with a small portion returning through the collector electrode and resistor 112 to ground. The major return flow of input signal current,l however is through the emitter electrode of TR and brush B1, to ground. From ground, the combined return flow to generator 500 is through the 10,000 ohm resistor PR, brush B9, and conductor 143. This 1000-` cycle input current ca uses a responsive 1000-cycle output signal current which flows in a path from ground, to the collector electrode by way of the emitter andv base electrodes, and is thence through brush B3 and the 10- ohm resistor 11-2,` to ground. In order to obtain an outputcurrent voltage reading on voltmeter 400, key K-4 is operated to lconnect the ungrounded terminal of the 10 ohm resistor 112 (in the output circuit) to the input wire 141 of voltmeter 400. The output of generator 500 may be again adjusted for a suitable Voltage which gives distortionless output signal-current, and voltmeter 400 is adjusted to give a convenient reading, as described.

Key K-4 is then. released to reconnect the voltmeter input wire 141 to the slide arm of resistor PR, which is in the traced input circuit. The slide arm of PR is now adjusted to givethe same reading on meter-400 for the input signal current as that obtained for the output signal current.

With the slide arm of PR calibrated from 0 to 1 as assumed, since the 10,000-ohm output'current resistance at PR is 1000 times the l0ohm input-current resistance at 112, the' reading of PR is multiplied by 1000. Thus, a full-scale reading at PR, if obtained on this test, would show a grounded-emitter current-gain factor B of 1000, whereas junction transistors as commonly produced do not provide gain factor B of more than 300, 4and usually less.

Test 3: Base resistance Rb.-Referring now to Figsfl and 4, brushes B1 to B9 of switch 120 are moved to 'their contacts P-3 of Fig. l, to position the test set for te'st 3, to measure the base resistance Rb, and generator key K-5 is operated to transfer generator wires from the secondary winding of S04, to the direct higher Voltage output of amplifier S02, by way of the 100,000-ohm limiting resistor 505, thereby enabling generator output appropriate to the test yto be obtained.

In test position 3, output conductor 143 of generator 500 vis connected to ground through brush B9 and the LOGO-ohm resistance combination comprising the 1,100- ohm resistor 111, with which the 10,000-ohm resistor PR is parallelly connectedby brushes B7 and B8. Current from generator 500 now flows over the generator output conductor 142, brush B3, and through the collector and base electrodes, to ground through brush B2.

Key K-4 is now operated to transfer voltmeter wire 141, through brushes B4 and B1, to the emitter electrode A of TR. The voltage drop to ground of the input current through the resistance of the base element appears' on the emitter electrode, and thus reaches the voltmeter 400. v

The output of generator 500 may be again adjusted for a suitable sine wave at 600, and voltmeter 400 is ad justed -to give a convenient reading, as described.

Key K-4 is now released to reconnect voltmeter 400 to the slide arm of resistor PR, and this slide arm is adjusted to give the same reading on voltmeter 400 as4 with key K-4 operated. l

With the assumed calibration of the slide arm of resistor PR from 0 to 1 and since the parallel resistance of 111 and PR (in the input path) is 1,000 ohms, the reading of PR is multiplied by 1,000 to give the ohmic value of the base resistance Rb.

Testv 4: Emz'tter resistance Re.-Referring now to Figs. 1 and 5, brushes B1 to B9 of switch 120 are moved to their contacts P-4 of Fig. 1, to position the test set for test 4, to measure the emitter resistance Re as hereinbefore defined, and the generator key K-5 isl left (or placed) in operated position as for test 3.

As'in test 3, output conductor 143 of generator 500 is connected to ground through brush B9 and the 1,000- ohm parallel resistance combination comprising-resistors PR and 111, but voltmeter conductor 141 is now connected through brush B2 to the base electrode to enable the drop across the emitter barrier and the emitter electrode, in series, to be impressed on voltmeter 400.

The generator current ythrough resistors '111 and PR has its return circuit through the three electrodes of TR 7 in series, to ground by way of brush B1, and thus does not traverse the base-electrode terminal B.

vWhen key `K4 is now operated, it connects v'oltmeter conductor I141 through brushes B4 and B2 to the base electrode of transistor TR The voltage drop to ground through Vthe emitter barrier and the emitter electrode, in series 'is thus placed'on Wire 141.

Withgthe `generator lcurrent and the reading Io'f voltmeterV 400 adjusted yas described, key lK-t is released 'to transfer the voltmeter wire to the slide `arm of PR, which is now adjusted to give the same voltrneter reading as with `K-'4 operated.

As `pointed out for test 3, the assumed scale lreading of the 'slide arm of PR is multiplied by 1,000 to give the ohmic value of the emitter resistance Re.

Test Collector resistance Zia-Referring to Figs. l and 6, the brushes B1 'to B9 are moved :to their-contacts P-S to yposition the test set to measure the collector resistance Rc. Generator-output ykey vK-S is restored (or left restored) to connect generator Wires 142 and 143 to the low-voltage secondary winding of transformer 51M, thereby giving a `low-impedance output of substantially constant Voltage, ras in all tests except Nos. 3 :and 4.

Key K-4 is now operated, closing the following path for generator current: From ground through brush B9, generator 500, brush B5, alternate contact of K-4, brushes B4 and B3, 'collector an'd base electrodes of TR, 'and thence to ground through ratio switch 700, one of .the Aresistors llaa-114C, and the lO-ohrn resistor 1'15. If 'ratio switch 700 is on its `ltlO-to-l-ratio Contact 2, the 990-ohm resistor' 114i: is in circuit, and the voltage drop across the 100G-ohm series resistance of 1Mb and 115 is impressed on meter 400 through brush B5. Amplitier 502 and attenuator 401 are ynow adjusted to give 'a desired reading on voltmeter 404. Then, one portion of the voltage of generator 500 is across the shunted Voltmeter 400, with the remainder across the collector resistance lof TR.

The key lK-t is now released, thereby transferring the generator 500 from the collector circuit of TR to a circuit path through the slide arm of PR, the low-'scale portion of PR, brush B7, and the -ohm resistor 1-15, to ground. The voltage drop across the lO-ohrn resistor 115 is now impressed on voltmeter 400 through resistor 11:4b and brush B5. PR, acting as a series load resistor, is now adjusted to give the same voltage-drop reading on voltmeter 400 across the lO-ohm resistor 115 as Ithat obtained (with key K-4 operated) across the 100G-ohm combination of 114b 'and 115. With the adjusted equal voltage readings, the current now owing through PR is 100 times (or 100G/10) the current through the collector -path, but the voltage drop across PR is the same a`s :that across the collector resistance with K-4 operated. Consequently, the tested collector resistance of TR is '100 times the adjusted resistance of PR. Since the adjusted resistance of PR is 10,000 ohms, the lmaximum observable collector resistance, when switch 700 is on its Contact 2,'as shown, is ten times that value, lor 1 megohm, which is 'in excess of the collector 4resistance encountered fornmost junction transistors.

The l-to-l-ra'tio position l of ratio switch 700 is preferred when the collector. path has a sufficiently low resistance 'that the voltage-drop-across the 100ohin"series combination of resistors 11la and 115 (with 'K-4 0perated) is enough to give a satisfactory test reading :at 400. The resistance ratio is vnowrl() to l since the 9'0- olirn Yresistance of 114a, plus the 10-ohm of 115, is ten times the resistance of y115 alone. A 100,000-ohm reading may be thus obtained.

lThe IOOO-tO-l-ratio position 3 'of ratio switch 760 'is forus'e'only when the resistance value under test is so high (above one rnegohm) that a comparative reading cannot `be obtained with position 1 or 2 'of 700. lIn posit tion 3, Ithe' drop in test resistance (with K-'d operated) is through 'the 10,()G0aohrn series resistance 'of 114C and 115, which is 1000 times the comparing drop through" the 10-ohn'1 'resistor `115. A yIO-megohm reading may thus be obtained.

. Test 6.' `Effective series resistance Res.`-Referring 'to Figs. 1 and 7, brushes Bl to B9 are placed in position 6 to iposition the ftest set to measure lthe -eective series resistance Res of TR. Test 6 is similar to test 5 errceptthat, with K-d depressed in test 6, the return 7path 'to ground for vgenerator 50) is through the emitter diode and brush B1, rather than directly from ythe -base electrode and brush B-Z, as in test 5, whereby the emitter diode is connected in series with the 'collector' diode 4to enable the effective resistance of the two diodes lin series to be ascertained. As in test 5, the ratio switch 700 Iis' preferably seton the appropriate one lof its 'three contacts to include `the lowest-valued one of the multiplying resistors `ltllla to 114C which will suice. I

The erlective series resistance as 'ascertained lin Itest 6 is less than the surn of the'ernitter yand collector resistlances, as separately ascertained in tests 4 and 5, by an amount depending 'upon the ability, in the `transistor under test, of the signal current through the emitter diode to generate (by the usual vresistance variations). a resultant signal voltage at the collector barrier. The resultant signal voltage, being in phase with the current, is in 'phase with the voltagespplied by generator400, and the two voltages are thus additive. The current is thus increased with respect to the voltage of generator 500,' thereby giving a `measured series-resistance value for 'Res which is less than the actual resistance of the path by an amount 'depending upon the value of the said resultant voltage. The amount by which the actual series resistance and the effective series resistance of TR differ is its so-called mutual resistance, which is given by the formula, Rr`n=E0/Ii, where Eo 'is the output signal voltage resulting 'from an input signal current through lthe emitter diode, and where It' is that input current. Thus, if Ref is the test-6 value ofthe effective series resistance, then Rm equals (Re plus Rc) minus Ref.

A high value obtained in test 5 for collector resistance RC, may be inaccurate because of small leakage paths and stray capacitances. Then, a moreaccurate Value Vfor Re may be calculated by using the result of test 6 and the vresult of either test 1 or test 2 in a well-known formula. Thus, while the result of test 5 or of test`6 can be calculated from the'results of other tests Where vaccuracy is not in doubt, 'the actual 'results of tests 5 and -6 permit each other to be checked -in comparison with 'the results of other ones of thesix tests.

SUMMARY on PROCEDURES-TESTS 1 To e yImportant `points in the foregoing 'tests 1 to 6 maybe summarized as follows: I

(l) .Generator voltage-In tests 1-, 2,v Y5,' ando, 'output key K-S o'f (generator 500 is 'in its illustrated norma1-position, Wherein'wires 142,"and 143 and supplied through fthe low-turn secondary of step-down transformer 504, "to provide a so'urce'of voltage which remains substantially constant under the load variationsjencountered during these tests. But, in tests y3 and '4 the output key K-'S is operated to transfer generator Wires 142 and l14,3 to the relatively high-voltage output of amplierSZ, since a high voltage (not required to be uniform under varying loads) is required to drive enough current through the collector resistance to enable the resulting voltage drop across the relatively low base or emitter resistance to 'be accurately observed.

(2) VoItmeter-tmnsfer tests 1 t0 4.--In tests 1 to 4, generator 500 supplies current to a single path which includes two of the electrodes of the transistor TR vin series with a comparison resistance combination which includes, or comprises, the adjustable precisionresistor PR. Also, a test conductor (at B4) is connected to the tliird electrode of TR, from which a reading is 4taken on v'oltmeter 400, with K-4 operated. When Kil 'is released, voltmeter-input wire 141 is transferred to the comparison resistance combination, and resistor PR therein is adjusted to give the same reading on voltmeter -400 as with key K-4 operated.

In each of the tests 1 to 4, the test voltage taken olf the noted third electrode of TR is the drop across a resistance. For tests 1 and 2, where input and output currents are compared, this dropping resistance is the known ohms of resistor 112. For tests 3 and 4, where resistances are compared to nd the resistance of a desired portion of TR, the noted dropping resistance is the resistance of that portion.

In all four of the tests 1 to 4, PR is used as a potential divider, and the comparison setting (for an equal reading at 400) is made by sliding the calibrated arm of PR. As explained for the respective tests, the comparison setting of PR is interpreted as indicating a current ratio or as indicating a resistance value, and that setting is multiplied by a suitable factor according to the circuit connections involved. v

(3) Generator-transfer tests 5 and 6.-In tests 5and'6, instead of providing a single path for current from generator 500 and transferring the voltmeter from one voltage-drop point to another as in tests 1 to 4, two paths for generator current are provided, and are closed alternatively (by key K-4), while the voltmeter remains connected to the same points for both testing and comparing. At those points, it is connected across the series combination `of resistor 115 which is common to both paths, and the one of the resistors 114a to 114C which is inserted in the test path by ratio switch '700. Thus, the txedly connected voltmeter 400 receives the drop across -resistor 114 and resistor 11S in series when the test path is closed, but receives the drop across alone when the comparing path is closed, whereby the multiplication factor for which switch 700 is set is obtained with a iixedly connected voltmeter.

(B) Junction type PNP test The foregoing tests 1 to 6 for the NPN junction transistor TR may be performed in the same way for a PNP junction transistor connected to terminals E, B, and C, except that key K-l is actuated to reverse the biasing potentials applied to the emitter and collector electrodes E and C. With key K-l operated, resistor 204 is adjusted to cause meter 206 to read according to the desired emitter bias, and resistor 203 is adjusted until meter 205 shows the desired bias current through the collector electrode. Contacts 3 to 8 of K-l reverse the connections to electrolytic blocking condensers 104 to 106 to correspond to the reversed polarity of bias current.

(C) Point-contact transistor test A point-contact transistor may be tested as described for junction transistors by connecting its electrodes to terminals E, B, and C. For the described tests 1 and 2, however, some point-contact transistors may oscillate, or nearly so, because of interaction between the input and output circuits across the higher base resistance of such transistors. An additional, or compensating resistance must therefore be introduced in the input and/ or output signal circuits.

The test set of Fig. 1, while designed primarily for testing junction transistors, is shown adapted for the testing of point contact transistors through the second set of test terminals E', B, and C', together with the adjustable series emitter resistor ER and the adjustable collector resistor CR. Resistors ER and CR are set to 'respective resistance values according to the rating of the point-contact transistor to be tested through terminals E to C', and the resistors 203 and 204 are set to give the desired bias currents therethrough. The readings for the described tests l to 6 through terminals E', B', and C are corrected according to the adjusted resistance values at ER and CR.

I claim:

1. A transistor test set comprising, in combinatioxi, test conductors for the respective electrodes of a transistor to be tested, means including bias conductors for delivering bias current over the respective test conductors to said electrodes, respective alternating-current blocking devices serially connected in said bias conductors, means including signal conductors for carrying alternating signal current over the respective test conductors between the test set and the electrodes of the connected and biased transistor, respective direct-current blocking devices serially connected in the signal conductors, an alternatingcurrent signal generator, a precision resistor having two xed terminals and a slide-arm terminal, a high-impedance alternating-current voltmeter, a multi-conductor testposition switch and means for setting it into any desired one of a number of test positions corresponding respectively to desired predeterminedtests vof a connected transistor, tie conductors variously interconnecting the last said positions of the test-position switch with the nsaid signal conductors, signal generator, precision resistor, and voltmeter, according to the respective tests to which such positions correspond, one tie conductor being a reference conductor, said switch and certain of said tie conductors providing in any last said switch position a iirst path from the reference conductor through the fixed terminals of the precision resistor and said generator, in series, to a first said signal conductor, and providing a second path from said reference conductor to a second said signal conductor, one terminal of said voltmeter being connected to said reference conductor, and comparison means and means including said switch and other ones of said tie conductors rendering it effective in any last said test position for connecting the other terminal of the voltmeter alternatively to the slide arm of said resistor and to a third said signal conductor, said slide arm being movable to a position at which the voltmeter reads the same in both of said connected positions thereof.

2. In a transistor test set according to claim 1, multiplier resistors, and means including the said switch for selectively connecting them in shunt of the iixed terminals of the precision resistor in respective selected positions of the said switch.

3. In a transistor test set according to claim 1, a Waveform monitor and means for operatively associating it with the said voltmeter to display the wave form of the signal voltage received by the voltmeter.

4. In a transistor test set according to claim 3, means for regulating the output of the signal generator to secure a sine wave signal voltage at the voltmeter and monitor.

5. In a transistor test set according to claim 1, means for adjusting the sensitivity of the voltmeter to secure a convenient reading thereof.

6. In a transistor test set according to claim 1, a multiplying resistor and a dropping resistor, said test-position switch having at least one other position wherein it connects the voltmeter between a rst signal conductor and the reference conductor, and connects the multiplying resistor and the dropping resistor in series between said first signal conductor and the reference conductor, with the dropping resistor adjacent to the reference conductor, said test-position switch including means rendering said comparison means eiective to close two paths for said generator alternatively, one path being from the reference conductor to a selected second signal conductor, while the other path is from the reference conductor to the junction of the multiplying and dropping resistors by way of the slide-arm terminal and one ixed terminal of the precision resistor.

7. In a transistor test set according to claim 6, there being a plurality of said multiplying resistors, and switch means for selectively connecting them in series with said dropping resistor.

8. A transistor test set comprising, in combination,

three test conductors for respective electrodes of a `transistor to 'be tested,means including three bias conductors for delivering bias current over the respective test conductors to `said electrodes,` respective alternating-current-blocking devices serially connected in said bias con'- ductors, 4'means including three signal conductors for carrying alternating signal current over the respectivev test conductors between Vthe test set and the electrodes of the connected and bias transistor, 'respective direct-current blocking -devices serially connected in the signal conductors, a 'reference conductor, an alternating-current signal generator, `an alternating-current measuring device, land means including selective switching means -for connecting -the generator between the reference conductor and either selected one of a given two of the three Signal conductors, while connecting the reference conductor directly to the other one of Ithe said given two signal conductors and connecting the measuring device between the 1reference conductor and the third one ofthe three signal conductors.

9. A transistor test set comprising, in combination, three test conductors vfor respective electrodes of a transistor lto be tested, -means including three bias 'conductors for delivering bias current over the respective test con-v ductors to said electrodes, respective alternating-current blocking devices serially connected inv said bias conductors, means including three signal l conductors for carrying alternating signal current over the respective ytest con# ductors between the test set and theelectrovdes, of the connected and biased transistor, respective direct-current blocking devices serially connectedin the signal con-v References Cited in the Aiileof` this patent Production Tester, for ,Transistorsj ,-El'ectr onics magazine, volume 23, issue l0, October 1950, pp. 96-99. Test Techniques `for Transistors, Radio-Electronics magazine, volume 24, No. 3,' March 71953, pp. 78-80, 82, y84. 

